System, method and apparatus for mobile transmit diversity using symmetric phase difference

ABSTRACT

Communication is performed for a first communication device having a set of antenna elements. A quality-indication signal is received from a second communication device (e.g., a basestation). A complex weighting is calculated based on the quality-indication signal. A pre-transmission signal is modified based on the complex transmit diversity weighting to produce a set of modified-pre-transmission signals, wherein the modifications are symmetric by making approximately half the magnitude of the transmit diversity modification to one signal in a first direction, and approximately half the magnitude of the transmit diversity modification to the other signal in a second direction, opposite the first direction. Each modified pre-transmission signal from the set of modified-pre-transmission signals is uniquely associated with an antenna element from the set of antenna elements. The set of modified-pre-transmission signals is sent from the set of antenna elements to produce a transmitted signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/766,725, now allowed, which is a continuation in part application ofU.S. patent application Ser. No. 12/010,655, filed Jan. 28, 2008, whichis a continuation of U.S. patent application Ser. No. 11/711,630, nowissued as U.S. Pat. No. 7,327,801, which in turn is a continuation ofU.S. patent application Ser. No. 10/141,342, now issued as U.S. Pat. No.7,321,636.

This application also claims benefit of provisional patent applicationSer. No. 61/253,428, filed Oct. 20, 2009, provisional patent applicationSer. No. 61/295,971, filed Jan. 18, 2010, provisional patent applicationSer. No. 61/297,898, filed Jan. 25, 2010, and provisional applicationSer. No. 61/310,192, filed Mar. 3, 2010, all of which are incorporatedin their entirety by reference herein.

BACKGROUND OF THE INVENTION

The invention relates generally to communications and more particularlyto a system and method for using a quality-indication signal added to atransmitted signal in a communication system, and used by the receivingend, in conjunction with multiple antenna elements. The receiver can usea separation process known as spatial filtering, or also referred toherein as smart antenna.

Broadband networks having multiple information channels are subject tocertain types of typical problems such as inter-channel interference, alimited bandwidth per information channel, inter-cell interference thatlimit the maximum number of serviceable users, and other interference.The usage of smart antenna techniques (e.g., using multiple antennaelements for a separation process known as spatial filtering), at bothends of the wireless communications channels, can enhance spectralefficiency, allowing for more users to be served simultaneously over agiven frequency band.

Power-control signaling is another technique used to minimizeinter-channel interference and increase network capacity. For example,mobile communication standards include a high rate, continuous,power-control signaling to ensure that mobile communication devices donot transmit too much or too little power. More specifically, based onthe strength of the signal sent from the communication device andreceived at the basestation, the basestation sends a power-controlsignal to the mobile communication device indicating whether thecommunication device should increase or decrease the total power of itstransmitted signal. The transmission rates for each value of thepower-control signals are, for example, 1.25 ms for cdmaOne(IS-95)/CDMA2000, and 0.66 ms for WCDMA.

The known uses of power-control signaling have been limited only toadjusting the total power of the signal transmitted from thecommunication device. Next generation communication devices, however,can use multiple antenna elements (also referred to herein as a “smartantenna”) for a separation process known as spatial filtering. Thus, aneed exists for an improved system and method that can combine theadvantages of power-control signaling with the advantages of smartantennas.

SUMMARY OF THE INVENTION

Wireless transmission systems may use transmit diversity, wherebysignals are simultaneously transmitted to a receiver using a pluralityof transmit antennas. A transmitting modifying communication device mayhave multiple antenna elements that transmit signals to communicateinformation. Multiple antenna elements for transmission may enhancespectral efficiency and capacity, allowing for more users to besimultaneously served over a given frequency band in a given single siteand or multiple cells area, and improving coverage, e.g., extending thereach and performance at cell edges, by adding additional transmittingantenna(s) to the UE in such a way that reduces destructive interferencebetween the various UE antennas (experienced at the base stationreceivers) which are caused by multi-path and fading. According toembodiments of the present invention, the plurality of signals may betransmitted differing by a transmit diversity parameter, e.g., a phasedifference, a power ratio, etc.

In mobile transmit diversity devices, communication is performed using aset of antenna elements. A quality-indication signal received from asecond communication device (e.g., a basestation) may be used as afeedback signal to adjust the transmit diversity parameter. Thequality-indication signal may include one or more power control bits, orreverse power control signal, provided by a base station over thedownlink to a mobile terminal as feedback for a transmit diversityparameter or other possible quality indicators originated by the basestation. A complex weighting, e.g., one or more transmit diversityparameters, is calculated based on the quality-indication signal. Amodulated pre-transmission signal is modified based on the complexweighting to produce a set of modified pre-transmission signals. Eachmodified pre-transmission signal from the set ofmodified-pre-transmission signals is uniquely associated with an antennaelement from the set of antenna elements. The set of modifiedpre-transmission signals is sent from the set of antenna elements toproduce a transmitted signal. The complex weighting is associated withtotal power of the transmitted signal and at least one from a phaserotation and a power ratio associated with each antenna element from theset of antenna elements.

According to particular embodiments of the invention, a transmitdiversity parameter may be phase difference between a plurality ofantennas. That is, a phase difference or phase rotation, between thesignals transmitted on the two or more antennas may be adjusted toimprove reception at the base station, e.g., increase signal strengthand or Quality by constructive combining of the received signals at thebase station. However, mobile transmit diversity communication devicesand methods must generally be adapted to operate in conjunction withpre-existing receivers, e.g., base stations designed for mobile transmitnon-diversity devices and methods. Embodiments of the present inventionprovide for mobile transmit diversity devices and methods that arecompatible with base station communication protocol in a manner as toreduce possible exposure of the base station to excessive environmentchanges that might deteriorate its channel estimation performance or SIRestimation or the interference cancellation performance as a result ofthe transmit diversity feature, or receiver equalization.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 shows a system block diagram of a communication network accordingto an embodiment of the invention;

FIG. 2 shows a system block diagram of a transmitter for the subscribercommunication device shown in FIG. 1;

FIG. 3 shows a system block diagram of a basestation and subscribercommunication device according to a known system;

FIG. 4 shows a system block diagram of a basestation and a subscribercommunication device having two transmitting antennas, according to anembodiment of the invention;

FIG. 5 illustrations a portion of the transmitter system for subscribercommunication device, according to another embodiment of the invention;

FIGS. 6A-6E are schematic figures illustrating transmit diversitysignals as received at a base station according to embodiments of theinvention;

FIGS. 6F-6G show schematic examples of an apparatus including a vectormodulator according to embodiments of the invention;

FIG. 7 shows a portion of the transmitter for the subscribercommunication device according to another embodiment of the invention;

FIG. 8 shows a transmitted portion of a subscriber communication deviceaccording to yet another embodiment of the invention;

FIG. 9 shows a flowchart for calculating the complex weighting byadjusting the phase rotation associated with each antenna element,according to one embodiment;

FIG. 10 shows a flowchart for calculating the complex weighting byadjusting the phase rotation associated with each antenna element,according to another embodiment;

FIG. 11 shows a flowchart for calculating the complex weighting byadjusting the phase rotation associated with each antenna element,according to yet another embodiment;

FIG. 12 shows a flowchart for calculating the complex weighting byadjusting the power ratio and the phase rotation associated with eachantenna element, according to an embodiment of the invention; and

FIG. 13 shows a flowchart for calculating the complex weighting byadjusting the power ratio and the phase rotation associated with eachantenna element, according to another embodiment of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A transmitted signal sent from a subscriber communication device (e.g.,a mobile communication device, or user equipment (UE)) to a secondcommunication device (e.g., a basestation) can be weakened by time or bypropagation-geometry-dependent fading and multipath. In other words, asignal sent from a subscriber communication device to a basestation willundergo destructive interference due to the fact that the transmittedsignal propagates along different paths and reaches the basestation as acombination of the signals each having a different phase.

Accordingly, by controlling the phase of the transmitted signal at thesubscriber communication device, the combination of signals received atthe basestation can be made to constructively interfere rather thandestructively interfere, or alternatively reduce the intensity of thedestructive interference. The phase of the transmitted signal can becontrolled through the use of multiple antenna elements at thesubscriber communication device. If the rate at which the transmittedsignal is controlled exceeds the rate of fading, then the basestationwill receive the transmitted signal at a relatively constant rate ofpower at a substantially optimized power. Because the rate of fading isrelatively slow (e.g., between few Hz and a couple of hundred Hz)compared to the rate of power-control signaling in certain knowncommunication protocols (e.g., around 1000s of Hz), power-controlsignaling can be used to tune a smart antenna to substantially optimizethe transmission of signals from a subscriber communication device to abasestation.

The tuning of the subscriber communication device is done through theuse of complex weighting. The signals associated with each antennaelement from a set of multiple antenna elements can be adjusted based onthe complex weighting. The term “complex weighting” relates to real andimaginary components of a signal, which can be varied to define themagnitude and phase of the signal. Because each of these signals can beadjusted differently, each signal is a low-correlation version of thepre-transmission signal upon which the transmitted signal is based. Inother words, the signals associated with each antenna element can beadjusted separately from each other based on the complex weighting sothat these signals are a low-correlation version of the pre-transmissionsignal. The signals transmitted on each antenna differ from others bysuch complex weighting, which may also be referred to as one or moretransmit diversity parameters. A transmit diversity parameter may be arelative phase difference between the signals, relative power ratiobetween the signals, etc. The complex weighting, e.g., the one or moretransmit diversity parameters, may be used to adjust the total power ofthe transmitted signal and/or the phase rotation and/or power ratioassociated with the signal transmitted on each antenna element. Thetransmit diversity parameter may be determined by a processor, forexample, based on one or more quality-indication signals, and applied tothe signals transmitted over the plurality of antennas by a vectormodulator, as described below.

Note that term “quality-indication signal” is used herein to mean asignal having information about the quality of the communication linkbetween a communication source sending the signal with multiple antennaelements and a communication device receiving the signal. For example,the quality-indication signal can be a power-control signal according toa code-division multiple access (CDMA) protocol. Such a CDMA protocolcan be, for example, CDMA-IS-95 A/B, CDMA 2000 1X/RTT, CDMA 2000 3X,CDMA EV-DO, wideband CDMA (WCDMA), third-generation (3G) UniversalMobile Telecommunications System (UMTS) and fourth-generation (LTE UMTSand or WiMAX). In fact, although the embodiments described herein areoften in reference to such a power-control signal, any type ofquality-indication signal in accordance with any type of communicationprotocol can be appropriate.

In addition, although the embodiments described herein are in referenceto a basestation sending a quality-indication signal to a subscribercommunication device having multiple antenna elements, alternativeembodiments are possible. For example, in alternative embodiments, aquality-indication signal can be sent from a subscriber communicationdevice to a basestation having multiple antenna elements. Alternatively,a quality-indication signal can be sent from one communication device toanother communication device having multiple antenna elements.

FIG. 1 shows a system block diagram of a wireless communication networkaccording to an embodiment of the invention. As shown in FIG. 1, network100 is coupled to basestation 110, which includes antenna 111.Subscriber communication device 120 is coupled to basestation 110 by,for example, a wireless communication link 130. Subscriber communicationdevice 120 includes baseband subsystem 121, quality-indication basedsignal modifier 122, radio subsystem 123, receive antenna 124, array oftransmit antennas 125, and application subsystem 126, which handles thevoice/data/display/keyboard, etc. The baseband subsystem 121 comprisestwo main portions: a modulator 140 and a demodulator 129. The radiosubsystem 123 comprises two main portions: a receiver 127 and amulti-channel transmitter 128.

Baseband subsystem 121, quality-indication based signal modifier 122,the multi-channel transmitter 128, and transmit antenna array 125 areportions of a transmitter for subscriber communication device 120.

Baseband subsystem 121 is the portion of the wireless communicationssystem that receives a modulated received signal 141, demodulates it toproduce demodulated received signal 142 and to extract the qualityindicator sent from the other side of the wireless link 130. Demodulatedreceived signal 142 is provided to application subsystem 126. Theextracted quality indicator is fed into the quality-indication basedsignal modifier 122 via quality-indication signal 143.Quality-indication based signal modifier 122 modifies thepre-transmission signal 145 in such a way that the other side of thewireless link 130 (e.g., basestation 110), undergoes improved receptionwithout necessarily increasing the combined power level transmitted fromthe subscriber communication device 120. Rather, by manipulating theweights of the various power amplifiers that feed their respectiveantenna elements in the array of transmit antennas 125, better multipathbehavior is achieved at the other side of the wireless link 130 (e.g.,at basestation 110), as explained in further detail below. Said anotherway, application subsystem 126 receives information for transmissionsuch as, for example, data and/or voice information. Applicationsubsystem 126 sends an unmodulated transmission signal 144 to modulator140 of baseband subsystem 121. Modulator 140 modulates unmodulatedtransmission signal 144 to produce pre-transmission signal 145, which isprovided to quality-indication signal modifier 122. Quality-indicationsignal modifier calculates a complex weighting based on thequality-indication signal 143 and modifies the pre-transmission signalto produce a plurality of modified pre-transmission signals 146. Eachmodified pre-transmission signal is uniquely associated with an antennaelement from the array of transmit antennas 145. The modifiedpre-transmission signal 146 is sent to multi-channel transmitter 128,which forwards the modified pre-transmission signals 146 to the array oftransmit antennas 125. The array of transmit antennas 125 sends aneffective combined transmitted signal based on the modifiedpre-transmission signal 146.

FIG. 2 shows a system block diagram of a transmitter for the subscribercommunication device shown in FIG. 1. The transmitter system 200includes baseband subsystem 210, quality-indication based signalmodifier 220, radio subsystem 230, power amplifiers 241, 242, 243 and244, and antenna elements 251, 252, 253 and 254. Baseband subsystem 210,quality-indication based signal modifier 220, radio subsystem 230,antenna elements 251, 252, 253 and 254, correspond to baseband subsystem121, quality-indication based signal modifier 122, radio subsystem 123,and transmit antenna array 125, shown in FIG. 1.

Note that although the subscriber communication device is shown FIG. 2as having four antenna elements 251 through 254 and four correspondingpower amplifiers 241 and 244, any number of two or more antenna elements(and corresponding power amplifiers) is possible. Thus, it will beunderstood that although the subscriber communication device isdescribed herein as having four antenna elements, other embodiments canhave any number of two or more antenna elements.

Baseband subsystem 210 is coupled to quality-indication based signalmodifier 220 and sends a pre-transmission signal 260 and aquality-indication signal 270. Quality-indication based signal modifier220 includes vector modulator 221 and control logic 222.Quality-indication signal modifier 220 is coupled to radio subsystem 230and power amplifiers 241 through 244. More specifically,quality-indication based signal modifier 220 provides modifiedpre-transmission signals to radio subsystem 230. Control logic 222 ofquality-indication based signal modifier 220 provides complex weightingto vector modulator 221 and power amplifiers 241 through 244, asdescribed below in further detail.

Radio subsystem 230 receives the modified pre-transmission signal fromquality-indication based signal modifier 220. The modifiedpre-transmission signal can be, for example either baseband signals, IFsignals, or RF signals. Radio subsystem 230 converts the receivedpre-transmission signal into radio frequency (RF) signals, which areprovided to power amplifiers 241 through 244.

Power amplifiers 241 through 244 each receive RF modifiedpre-transmission signals and amplify those signals for transmission.Power amplifiers 241 through 244 are coupled to antenna elements 251through 254, respectively. Power amplifiers 241 through 244 provide theamplified signals to antenna elements 251 through 254, each of whichsends its respective RF modified pre-transmission signal to produce atransmitted signal. In other words, each antenna element 251 through 254sends a respective signal component all of which form a transmittedsignal.

FIG. 3 shows a system block diagram of a basestation and subscribercommunication device according to a known system. This is helpful forunderstanding how prior CDMA basestation systems employ a power-controlsignal to adjust the transmit power of the subscriber communicationdevice.

In FIG. 3, basestation 300 includes receiver (Rx) 310 and transmitter(Tx) 320. Receiver 310 includes demodulator 312, signal-to-noise ratio(SNR) or RSSI (RF Signal Strength Indicator) estimator 313 and powercontrol bit generator 314. Receiver 310 is coupled to antenna 311.Transmitter 320 includes modulator 321, multiplexer 322 and poweramplifier (PA) 323. Transmitter 320 is coupled to antenna 324.

Subscriber communication unit 350 includes receiver 360, transmitter370, duplexer/diplexer 380 and antenna 390. Duplexer/diplexer 380 cancomprise a filter separating different bands like cellular serviceversus Personal Communication Service (PCS), and/or separation ofreceive/transmit; typically, duplexer/diplexer 380 has one portconnected to one antenna, and other port connected to various radiocircuitries that operate either simultaneously or alternatively.Receiver 360 includes demodulator 361. Transmitter 370 includesmodulator 371, power control logic 372, power amplifier (PA) 373 andradio subsystem 374.

Antenna 311 at the basestation receiver 310 is coupled to demodulator312, which is in turn coupled to SNR or RSSI estimator 313. SNR or RSSIestimator 313 is coupled to power control bit generator 314, which is inturn coupled to multiplexer 322. Multiplexer 322 is also coupled tomodulator 321 and power amplifier (PA) 323, which is in turn coupled toantenna 324.

Antenna 390 at the receiver 360 of subscriber communication device 350is coupled to duplexer/diplexer 380. Duplexer/diplexer 380 relaysreceived signals from antenna 390 to receiver 360 and relays signalssent from transmitter 370 to antenna 390. More specifically,duplexer/diplexer 380 is coupled to demodulator 361, which is coupled topower control logic 372.

Turning to the transmitter 370, modulator 371 receives thepre-transmission signal for transmission and provides it to radiosubsystem 374. Radio subsystem 374 converts the pre-transmission signalinto a RF signals, and forwards it to power amplifier 373. Poweramplifier 373 is also coupled to power-control logic 372, which providespower-control information. More specifically, the received signalsinclude a quality-indication signal such as, for example, apower-control signal having one or more power-control bits. Thesepower-control bits indicate the manner in which the subscribercommunication device should modify the total power of the transmittedsignal. The power control indication is originally generated at theother side of the wireless communications link (e.g., basestation 300),and is sent back to the subscriber communication unit 350 to obtainimproved signal quality in such a way that will produce reducedinterference. These power-control bits are provided to power amplifier373, which adjusts the total power for the transmitted signal based onthe power-control bits. Power amplifier 373 is coupled toduplexer/diplexer 380, which forwards the amplified pre-transmissionsignal to antenna element 390 for transmission.

Note that in the known subscriber communication device 350, the powercontrol logic 372 provides information based on the received powercontrol bit to power amplifier 373. The only adjustment to the transmitsignal is an adjustment to the power amplifier output level.

FIG. 4 shows a system block diagram of a basestation and subscribercommunication device according to an embodiment of the invention.Basestation 400 includes a receiver (Rx) 410 and transmitter (Tx) 420.Receiver 410 includes antenna 411, demodulator 412, SNR or RSSIestimator 413 and power control bit generator 414. Transmitter 420includes modulator 421, multiplexer 422, power amplifier (PA) 423 andantenna 424.

Subscriber communication unit 450 includes receiver 460, transmitter(Tx) 470, dual duplexer/diplexer 480 and antennas 490 and 495. Dualduplexer/diplexer 480 is, for example, a set of two units, eachcomprising a duplexer/diplexer. Receiver 460 includes demodulator 461.Transmitter 470 includes quality-indication based signal modifier 475,which includes vector modulator 471 and power control logic 472.Transmitter 470 also includes radio subsystems 476 and 477, and poweramplifiers 473 and 474.

Antenna 411 at the basestation receiver 410 is coupled to demodulator412, which is in turn coupled to SNR estimator 413. SNR or RSSIestimator 413 is coupled to power control bit generator 414, which is inturn coupled to multiplexer 422. Multiplexer 422 is also coupled tomodulator 421 and power amplifier 423, which is in turn coupled toantenna 424.

Subscriber communication unit 450 includes antennas 490 and 495 that areused for both reception and transmission, and are coupled to dualduplexer/diplexer 480. Dual duplexer/diplexer 480 is coupled to receiver460 and transmitter 470. Note that for the purpose of this embodiment,the receiver may use only one of the two antennas 490 and 495, or acombination of them. Receiver 460 includes demodulator 461, which iscoupled to control logic 472 of quality-indication based signal modifier475. Control logic 472 is coupled to vector modulator 471 ofquality-indication based signal modifier 475. Vector modulator 471 iscoupled to radio subsystems 476 and 477, which are coupled to poweramplifiers 473 and 474, respectively. Power amplifiers 473 and 474 arealso coupled to control logic 472. In addition, power amplifiers 473 and474 are coupled to antenna elements 490 and 495, respectively, throughdual duplexer/diplexer 480.

Demodulator 461 receives signals from antennas 490 and 495 via the dualduplexer/diplexer 480 to produce a quality-indication signal. Thisquality-indication signal can be, for example, a power-control signalhaving one or more power-control bits. This quality-indication signal isprovided to control logic 472. Note that demodulator 461 performs otherfunctions and produces other signals, which are not shown in FIG. 4 forthe purpose of clarity in the figure. Control logic 472 produces complexweighting values and forwards these complex weighting values to vectormodulator 471 and power amplifiers 473 and 474. Power amplifier 473 isassociated with antenna element 490 and power amplifier 474 isassociated with antenna element 495.

Note that the control logic 472 is different from the power controllogic 372 of the known subscriber communication device 350 shown in FIG.3. The power control logic 372 merely provided power control informationto power amplifier 373, whereas the control logic 472 shown in FIG. 4provides complex weighting to both the vector modulator 471 and the setof power amplifiers 473 and 474. This allows not only the total power ofthe transmitted signal to be adjusted based on the receivedpower-control bit, but in addition, allows the phase rotation and/or thepower ratio associated with each antenna element 490 and 495 to beadjusted based on the received power control information. Accordingly,this allows the transmitted signal to be optimal with respect to itsreception by basestation 400. Once this optimized signal is received bybasestation 400, basestation 400 can then send a power-control signal tosubscriber communication device 450 indicating that subscribercommunication 450 should adjust the total power of its transmittedsignal. Consequently, by optimizing the transmitted signal, the totalpower of the transmitted signal can be reduced, versus the case of acommunication device with a single antenna, as described in FIG. 3. Suchan optimization beneficially allows, for example, an increase in thebattery lifetime of subscriber communication unit 450, an increase inthe cellular system capacity of the communication network, and adecrease in the radiation hazard to the user of the subscribercommunication unit 450.

The complex weighting provided by control logic 472 can be based on thetotal power of the transmitted signal and one or both of the phaserotation and the power ratio associated with each antenna element 490and 495.

FIG. 5 illustrates a portion of the transmitter system for subscribercommunication device, according to another embodiment of the invention.Quality-indicator based signal modifier 500 includes control logic 502,analog-to-digital (A/D) converter 504, vector modulator 506 anddigital-to-analog (D/A) converters 508 through 509. D/A converter 508 iscoupled to radio subsystem 510 and D/A converter 509 is coupled to radiosubsystem 512.

Note that the D/A converters and radio subsystems are repeated for anumber that corresponds to the number of antenna elements. In otherwords, if subscriber communication device has N number of antennaelements, then the subscriber communication device has N number of D/Aconverters and radio subsystems. Thus, as shown in FIG. 5, D/A converter508 and radio subsystem 510 are associated with one antenna element froma set of antenna elements (not shown in FIG. 5). D/A converter 509 andradio subsystem 512 are associated with a different antenna element fromthe set of antenna elements. Any remaining antenna elements from the setof antenna elements are each also uniquely associated with a D/Aconverter and a radio subsystem.

The quality-indicator based signal modifier 500 receives an IFpre-transmission signal and power-control signal. The IFpre-transmission signal is received by A/D converter 504, which convertsthe analog pre-transmission signal to a digital form. The A/D converter504 forwards the digital pre-transmission signal to vector modulator506. The power control signal is received by control logic 502, whichdetermines complex weighting values.

The complex weighting is calculated by determining the appropriateweighting value associated with the in-phase signal component and thequadrature signal component associated with each antenna element. Forexample, in the case where the phase rotation is being adjusted, theweighting value for the in-phase signal component will be different thanthe weighting value for the quadrature signal component. In the casewhere the power ratio is being adjusted, the weighting value for thein-phase signal component and the weighting value for the quadraturesignal component are simultaneously increased or decreased for a givenantenna element in parallel. Finally, in the case where the total powerof the transmitted signal is being adjusted, the weighting value for thein-phase signal component and the weighting value for the quadraturesignal component are simultaneously increased or decreased for all ofthe antenna elements in parallel.

Control logic 502 provides the complex weighting values to vectormodulator 506. Vector modulator 506 receives the digitalpre-transmission signal from A/D converter 504 and the complex weightingvalues from control logic 502. Vector modulator 506 splits thepre-transmission signal into a number of pre-transmission signalscorresponding to the number of antenna elements. The vector modulator506 then applies the complex weighting to the various pre-transmissionsignals so that each pre-transmission signal, which uniquely correspondsto an antenna element, modifies the respective pre-transmission signalbased on the complex weighting values. The modified pre-transmissionsignals are then provided to D/A converters 508 through 509, whichconvert the pre-transmission signal from digital to analog form. Thosepre-transmission signals are then provided to radio subsystems 510through 512, respectively, which then convert the IF form of thepre-transmission signals into an RF form. These signals are thenforwarded to power amplifiers and respective antenna elements (not shownin FIG. 5).

It will be recalled that the base station may perceive the transmissionsas a single combined signal. That is, the base station may receive thetwo or more transmit diversity signals as a single signal having anamplitude and phase. The characteristics of the combined transmitdiversity signals as received by the base station are referred to hereinas the perceived characteristics. Thus, for example, the mobile transmitdiversity communication device may transmit first and second signalswith a phase difference therebetween. These first and second signals maybe perceived at the base station as a combined signal having a perceivedphase and a perceived amplitude. Moreover, the paths of the signalstransmitted by the antennas of the mobile communication devicerespectively, may be subject to different fading e.g., different complexpath-loss. Thus, the signal transmitted by one antenna may arrive at thebase station with a first phase shift, and the signal transmitted byanother antenna may arrive at the base station with a second phaseshift, different from the first phase shift. Thus, the phase andamplitude difference between the signals transmitted by the antennas maynot be (and typically is not) identical to the phase and amplitudedifference between the transmitted signals as perceived at the basestation. When received as a perceived combined signal at the basestation, therefore, the transmitted signals may combine constructivelyor destructively. This self interference operating on the signalstransmitted by the mobile unit's antennas may not be known a priori, andis not typically measurable by a base station. Therefore, embodiments ofthe present invention may use a gradient-seeking perturbation method, asdescribed herein in a number of variations, in order to determine anoptimal phase difference between the transmission signals, such thatwhen received, the signals combine constructively.

According to an embodiment of the invention, the processor or controllogic of the mobile communication device may output one or moreparameters to modify a pre-transmission signal by adjusting a nominalvalue of a transmit diversity parameter differentiating a first signalto be transmitted on a first antenna from a second signal to betransmitted on a second antenna. As described more fully herein,according to an embodiment of the invention, modulation of a transmitdiversity parameter during a perturbation cycle may comprisetransmitting using a transmit diversity parameter deviating from thenominal value in a first direction during a first portion of theperturbation cycle and then transmitting using a transmit diversityparameter deviating from the nominal value in a second direction duringa second portion of the perturbation cycle. Variations are possible, forexample, there may be a number of consecutive perturbations in a firstdirection over a number of slots, followed by a number of consecutiveperturbations in a second direction over a number of slots. In anothervariation, the mobile unit may change the transmit diversity parameterbased on a sequence of quality indicator feedback signals, etc. Othermethods of varying a transmit diversity parameter are possible withinthe scope of the present invention.

According to one embodiment of operation of the invention, the mobilecommunication device may modify a signal by perturbing the signal.Perturbing a signal may refer to modulating a signal feature of thesignal in relation to a nominal value of the signal, for example,modifying the signal feature in a first direction for a first feedbackinterval, and in a second direction for another feedback interval. Aperturbation cycle may refer to a first modulation in a first directionand a second modulation in a second direction. In some embodiments ofthe invention, a perturbation cycle may comprise a different, e.g.,longer or more complex, sequence of modulations. As an example withrespect to an embodiment of the invention in which the transmitdiversity parameter is relative phrase rotation, or phase difference, aperturbation may include modulating the phase difference in a firstdirection, and modulating the phase difference in a second direction. Ifthe feedback information provided by the feedback communication device,e.g., base station, indicates an improvement in the signal receivedusing one perturbation modulation direction compared to the signalreceived using the other perturbation modulation direction, the nextnominal value adjustment may be made in the improved direction in anamount that may be less than or equal to the modulation.

The signals transmitted by the antennas of the mobile station each havean amplitude and a phase. Accordingly, the signals may be schematicallydepicted as vectors having a positive scalar amplitude and a direction,or phase. For purposes of schematic simplicity, the phase may beregarded as an angle of the signal vector from the x-axis. Thus, asdescribed above, the signal vectors, e.g., amplitude and phase, of thetransmit signals may be known at the point of transmission, but themobile unit does not typically have access to either a priori (e.g.,theoretically calculated) or measured phase difference as perceived bythe base station. Rather, the base station provides a signal-qualityindicator based on the combined signal. It is an object of the mobiledevices and methods employed thereby according to embodiments of thepresent invention to calculate a transmit diversity parameter that whenapplied allows transmit signals to be perceived at the base station ashaving substantially no phase difference or at least to reduce thecomponent of the perceived phase difference, created by the phase changeof the mobile device, thereby allowing the signals to combineconstructively, in such a way that causes the base station tosubstantially perceive a different amplitude, with little or noperceived phase change. Conversely, it will be understood that a phasedifference of 180° as perceived at the base station is to be avoided orits occurrence should be minimized, insofar as this may cause thesignals transmitted by the antennas to destructively interfere, therebycausing the base station to perceive a weak or noisy signal.

It will be recognized that embodiments of the present invention may alsobe applicable for base stations that provide any sort of signal qualityfeedback. For example, a base station may provide a mobile unit withmore detailed information than simply a single-bit POWER UP or POWERDOWN signal; for example, a base station may propose to the mobile unita recommended next transmit diversity parameter. In such cases, thesymmetric change of phase difference of the present invention may stillapply. Thus, for example, where the base station may request aparticular change in phase difference, the mobile unit may implementsuch change in phase difference symmetrically over the antenna paths.

FIG. 6A is a schematic diagram of illustrative vectors symbolizing thetransmit signals being perceived as combined at the base station. Thus,signal vectors A and B represent the signals transmitted by antennas Aand B, respectively, as received at the base station, each with arespective amplitude (|A| and |B|) and phase (α and β). Known vectoroperations may be applied to obtain the amplitude (magnitude) and phase(angle) of the resultant signal (vector).

By placing the vectors head-to-tail, it will be apparent that theamplitude of the resultant vector has a maximum value when the phase ofA (as perceived at the base station) equals the phase of B (as perceivedat the base station), i.e., when the perceived phase differenceapproaches zero. Therefore, the perturbation schemes described hereinare intended to systematically attempt various phase differences andobtain feedback from the base station to determine whether the perceivedeffect of such changes in phase difference is to improve or deterioratea signal quality indicator (e.g., signal power as perceived by the basestation receiver or the combination of active base stations). Where thesignal quality indicator indicates improvement in signal quality, it isinferred that the change caused the perceived phase difference todecrease, and where the signal quality indicator indicates deteriorationin signal quality, it is inferred that the change caused the perceivedphase difference to increase.

The feedback communication device, e.g., the base station, however, maykeep track of certain receive parameters of signals received from themodifying communication device, e.g., the mobile transmit diversitydevice, for example, for purposes of channel estimation, SIR estimation,and/or interference cancellation. One such parameter that may be trackedby the base station may be the phase of the received (combined) signalas perceived by the base station.

The base station may record a number of such receive parameters over thecourse of a plurality of slots, in order to detect and possiblyanticipate a trend in the receive signal. Abrupt or immediate changes ofsignal phase perceived by the base station may be disruptive to theoperation of the base station. Therefore, changes of a transmitdiversity parameter, particularly a phase difference, made in order toimprove receive signal quality may have the side-effect of disruptingcontinuity perceived by the base station, for example, by causing anabrupt or immediate change in perceived phase of the receive signal,even if the perceived phase difference is decreased.

FIG. 6B depicts a signal A transmitted by a first antenna, and signalsB1 and B2 transmitted in subsequent transmissions by a second antenna,where the phase of signal B1 is β1 and the phase of signal B2 is β2. Themagnitude of the combined vector A+B2 is greater than the combinedvector A+B1. However, the base station will perceive a change in thephase of the perceived signal, and may disrupt continuity at the basestation.

According to embodiments of the present invention, potential negativeimpact on the base station due to changes in perceived phase may bereduced. In some embodiments of the invention, the modification in atransmit diversity parameter may be implemented in such a way as toreduce or minimize disruption in continuity of perceived receive signalphase.

As described herein, in some embodiments of the invention, particularlyin a mobile transmit diversity device having two antennas, phase changesmay be applied for an offset mechanism as well as for implementing astep in the current nominal or center phase value, where the phase maybe perturbated monotonously and continuously back and forth, swinging infixed values and alternating signs sequence, identifying a preferreddirection, and modifying the center phase value accordingly, thuspromoting a gradient-seeking process. In accordance with the presentinvention, such phase changes may be implemented in such a way as toreduce or minimize disruption in continuity of perceived phase of thereceive signal.

In some embodiments of the invention, modification of a transmitdiversity parameter may be performed symmetrically, that is, bymodifying a parameter of a first transmit signal in a first direction,while simultaneously modifying a parameter of a second transmit signalin a second direction, such that there is little or no perceived effectat the base station.

For example, in the case of phase difference, the phase of the first andsecond signals may be adjusted by applying modifications to each of theplurality of antennas, rather than solely to one of the signals. Moreparticularly, according to some embodiments of the invention, in orderto achieve a particular phase difference, the phase of the first signalmay be adjusted in approximately half the desired phase difference in afirst direction (e.g., positive), the phase of the second signal may beadjusted in approximately half the desired phase difference in a seconddirection (e.g., negative), opposite to the first direction. Theperceived phase effect of the applied transmit diversity phasedifference may thereby be minimized or even eliminated, for example, incases where the power levels of the two transmitting antennas areperceived as equal by the base station receiver.

In some embodiments of the invention, for example, if a phase change ofΔφ is desired, then the signal transmitted on one antenna branch may bemodified by Δφ/2, while the signal transmitted on another antenna may bemodified by −Δφ/2, thus effecting a full Δφphase change, while reducingor eliminating phase change as perceived by the base station. Next, insome embodiments of the invention, this will be followed by reversal ofthe branches, i.e., the branch that was previously modified by Δφ/2 willthen be modified by Δφ to −Δφ/2, and the other branch that waspreviously modified by −Δφ/2 will then be modified by Δφ to Δφ/2.Accordingly, a phase difference of Δφ between the two branches isachieved, thereby perturbing the transmit diversity parameter, therebyto obtain feedback information, while reducing or minimizing theperceived phase change from a previous perceived phase at the basestation. It will be recognized that such a reversal may repeat everytime phase change is applied.

An illustration of an embodiment of the present invention is depicted inFIGS. 6C, 6D, and 6E. FIG. 6C depicts two signals A and B, transmittedwith a particular arbitrary phase difference. The signals are eachreceived at a respective phase (α and β, respectively), resulting in areceived phase difference, which may typically be different than thetransmitted phase difference. For purposes of illustration, themagnitudes of signals A and B, as received at the base station isassumed to be approximately equal.

In a first perturbation, shown in FIG. 6D, the phase difference of thesignals is decreased symmetrically by offset or increment Δφ. Inparticular, signal A is transmitted at phase α+Δφ/2, and signal B istransmitted at phase β−Δφ/2. Thus, the phase of the combined signal asperceived by the base station difference as perceived by the basestation is identical in FIGS. 6C and 6D; however, the amplitude of thecombined signal has changed. In the depicted example, the combinedamplitude, or strength, of the combined signal has increased, which mayresult in an improved signal quality indicator being sent to the mobilestation.

In a second perturbation, shown in FIG. 6E, the phase difference of thesignals is increased symmetrically by an offset or increment Δφ. Inparticular, signal A is transmitted at phase α−Δφ/2, and signal B istransmitted at phase β+Δφ/2. Thus, the phase of the combined signal asperceived by the base station difference as perceived by the basestation is identical in FIGS. 6C and 6E; however, the amplitude of thecombined signal has changed. In the depicted example, the combinedamplitude, or strength, of the combined signal has decreased, which mayresult in a deteriorated signal quality indicator being sent to themobile station.

Accordingly, embodiments of the present invention may apply symmetricphase changes, e.g., offsets or increments, to the signals transmittedon the antennas, such that when equally added, the resultant sum ofthese phase changes will be small or zero. Such a summation maytherefore create a perceived amplitude change at the base station, withlittle or no perceived phase change, thereby reducing or minimizingdisruption in continuity of perceived receive signal phase at the basestation. The same mechanism may be applied to phase steps, e.g., whenthe algorithm derives from the monotonic perturbations a decision tostep the center phase up or down (towards a preferred calculateddirection).

In some embodiments of the invention, the transmit antennas may havedifferent efficiencies, which may result in unequal combining.Accordingly, when the two transmit signals are combined unequally, theamplitude change may be accompanied by a phase change as well, inproportion to the efficiencies ratio of the antennas. Thus, forinstance, according to embodiments of the invention, when theefficiencies of the antennas are not equal, then symmetry may becalculated based on a variation of the above, which may take intoaccount the different efficiencies. Thus, a proration similar to theaverage power imbalance may be applied to the ratio between the phasechange of one branch and the phase change of the other branch. Forexample:

${{\sin \; {\Delta\varphi}_{2}} = {{- \sin}\; {{\Delta\varphi}_{1}\left\lbrack \frac{\eta_{1}}{\eta_{2}} \right\rbrack}}},$

where η1 represents the efficiency of the first antenna, and η2represents the efficiency of the second antenna. Accordingly, thecombined complex vector will remain small or zero, and the phase changewill be perceived as small or none at the base station. A similarcalculation may be performed where the signals are transmitted withdifferent power by the respective antennas, e.g., where the power ratiois greater than or less than unity in inverse proportion to theantennas' respective inefficiencies.

In some embodiments of the invention, a phase difference Δφ may be acombination of an offset (referred as “δ”), which may be a perturbationmechanism, e.g., a systematic and monotonous equal amplitude andopposing signs that swing back and forth, and an optional step size(referred as “φ”), which is a change that is added to one branch onlyfrom time to time, per the algorithm decision making process. Thealgorithm decision may result in one of the following six possible phasechanges: ±δ, or ±δ±φ, i.e., {δ, −δ, δ+φ, δ−φ, −δ+φ, −δ−φ}. This phasedifference may be divided between the branches as δ/2 on one branch, and−δ/2 or −δ/2±φ on the other branch. Thus, for example, if the phasedifference is δ−φ, one branch may be modified by δ/2, while the secondbranch arm may be modified by −δ/2±φ. In another embodiment of theinvention, the phase difference maybe divided equally, particularlywhere the antennas have equal efficiencies. In the event the antennashave different efficiencies, the phase difference may be divided asprovided by the above equation.

FIG. 6F shows a system block diagram of an embodiment of vectormodulator shown in FIG. 5. Vector modulator 506 includes filter 610,in-phase signal adjusters 620 through 630, quadrature signal adjusters640 through 650, and combiners 660 through 670.

The in-phase signal adjuster 620, the quadrature signal adjustor 640 andthe combiner 660 are all uniquely associated with an antenna elementfrom the set of antenna elements (not shown in FIG. 6F). This set ofcomponents is repeated within vector modulator 506 corresponding to thenumber of remaining antenna elements for the subscriber communicationdevice. Thus, as shown in FIG. 6, in-phase signal adjuster 630,quadrature signal adjuster 650 and combiner 670 are also shown foranother antenna element of the subscriber communication device.

Filter 610 receives the digital pre-transmission signal from A/Dconverter 504. Filter 610 divides the received pre-transmission signalinto in-phase and quadrature components. The in-phase component of thepre-transmission signal is provided to in-phase signal adjusters 620through 630. The quadrature component of the pre-transmission signal isprovided to quadrature signal adjusters 640 through 650. In-phase signaladjusters 620 through 630 and quadrature signal adjusters 640 through650 receive complex weighting values from control logic 502. In-phasesignal adjusters 620 through 630 and quadrature signal adjusters 640through 650 apply the complex weighting to the pre-transmission signalcomponents to produce modified pre-transmission signals. In-phase signaladjusters 620 through 630 and quadrature signal adjusters 640 through650 provide modified pre-transmission signals to combiners 660 and 670,respectively. Combiners 660 and 670 then add the respective modifiedpre-transmission signals and forward the added signals to D/A converters508 and 509, respectively.

FIG. 6G depicts a schematic illustration of a symmetric vector modulatorfor producing symmetric changes in phase difference between signals onat least two antennas. A pre-transmission signal is input to the vectormodulator at the input node 675. The pre-transmission signal may besplit into at least two branches, one for each transmission antennapath. In one path, the amplitude of the signal is modified byamplification factor a, and the phase of the signal modified by e^(Jφ1).In a second path, the amplitude of the signal is modified byamplification factor √(1−a²), and the phase of the signal modified bye^(Jφ2). Assuming the amplitudes of the transmitted signals are equal,i.e., a=1/√2, and the antenna efficiencies are equal, then symmetricchanges δ in phase difference may be achieved by setting φ1=−δ/2 andφ2=δ/2, or another combination such that δ=φ2−φ1.

FIG. 7 shows a portion of the transmitter for the subscribercommunication device according to another embodiment of the invention.The transmitter portion shown in FIG. 7 receives analog baseband signals(labeled in FIG. 7 as “Baseband I Channel Data Signal (In)” and“Baseband Q Channel Data Signal (In)”) into a quality-indicator signalmodifier 700.

Quality-indicator based signal modifier 700 includes A/D converters 710and 715, filters 720 and 725, vector modulator 730, control logic 740,combiners 750 and 755, and D/A converters 760 and 765. D/A converters760 and 765 of quality-indicator signal modifier 700 are coupled toradio subsystem 770 and 780, respectively.

A/D converter 710 receives the baseband in-phase signal. A/D converter715 receives the baseband quadrature pre-transmission signal. A/Dconverters 710 and 715 are coupled to filters 720 and 725, respectively,which are in turn coupled to vector modulator 730. Control logic 740receives the power-control signal and forwards complex weighting valuesto modulator 730. Vector modulator 730 is coupled to combiners 750through 755.

Combiner 755, D/A converter 760 and radio subsystem 770 uniquelycorrespond to a given antenna element from the set of antenna elementsfor the subscriber communication device (not shown in FIG. 7). This setof components is also present corresponding to the number of antennaelements for the subscriber communication device. Consequently, combiner755, D/A converter 765 and radio subsystem 780 are also showncorresponding to a different antenna element from the set of antennaelements. Any number of additional sets of components can be presentcorresponding to the number of antenna elements.

FIG. 8 shows a transmitter portion of a subscriber communication deviceaccording to yet another embodiment of the invention. More specifically,FIG. 8 shows a quality-indicator signal modifier that receives basebanddigital signals.

Quality-indicator based signal modifier 800 includes vector modulator810, control logic 802, D/A converters 830, 835, 840 and 845, andcombiners 850 and 860. Combiners 850 and 860 of quality-indicator basedsignal modifier 800 are coupled to radio subsystems 870 and 880,respectively.

Control logic 820 receives a power-control signal and produces complexweighting values, which are provided to vector modulator 810. Vectormodulator 810 also receives a digital baseband in-phase pre-transmissionsignal and a digital baseband quadrature pre-transmission signal. Vectormodulator 810 splits the in-phase and quadrature pre-transmission signalcomponents into a number of signals that correspond to the number ofantenna elements for the subscriber communication device. The complexweighting values are then applied to the in-phase and quadraturepre-transmission signal associated for each antenna element from the setof antenna elements for the subscriber communication device to producemodified pre-transmission signals. These modified pre-transmissionsignals are then provided to D/A converters 830 through 845, whichconvert the digital form of the modified pre-transmission signals intoanalog form and forward these pre-transmission signals to combiners 850and 860, respectively. Combiner 850 receives the in-phase and quadraturecomponents of the modified pre-transmission signals from D/A converters830 and 835, respectively. Combiner 850 adds these two signals andforwards the added signal to radio subsystem 870. Similarly, combiner860 receives the analog in-phase and quadrature signal components of themodified pre-transmission signals from D/A converters 840 and 850,respectively and adds the signals. Combiner 860 adds these two signalsand forwards the added signals to radio subsystem 880.

FIG. 9 shows a flowchart for calculating the complex weighting byadjusting the phase rotation associated with each antenna element,according to an embodiment. Although FIG. 9 will be described inreference to FIGS. 1, 5 and 6 for convenience, the method described inreference to FIG. 9 can be used with any configuration of a subscribercommunication device. In addition, although the quality-indicationsignal can be any appropriate type of signal that provides informationto the subscriber communication device on the quality of the signal, forconvenience of discussion, the quality-indication signal is assumed beto power-control signal according to the CDMA protocol.

At step 900, a power-indication signal is sent from basestation 110 tosubscriber communication device 120 via wireless connection 130. At step910, the power-control signal is sent from the baseband subsystem 121 tothe quality-indicator based signal modifier 122 (also shown asquality-indicator based signal modifier 500 in FIG. 5). Thepower-control signal according to the CDMA protocol indicates one of twopossible values for any given time period: an “up” value or a “down”value. An “up” value represents an indication from the basestation tothe subscriber communication device that the subscriber communicationdevice should increase the total power of its transmitted signal. A“down” value represents an indication from the basestation to thesubscriber communication device that the subscriber communication deviceshould decrease the total power of its transmitted signal. Theparticular value of the power-control signal is also referred to hereinas including a power-control bit, which represents either the up or downvalues in binary form.

At step 920, the process is held until the power-control signal reachesa steady state. The power-control signal can reach a steady state in anumber of ways. For example, a consecutive sequence of power-controlsignals of up-down-up or down-up-down. Once the power-control signalreaches a steady state, the process proceeds to step 930.

At step 930, the phase rotation associated with one antenna element isadjusted. Returning to FIGS. 5 and 6, control logic 502 calculates a newcomplex weighting so that the phase rotation for one antenna element ischanged. This complex weighting is provided to the signal adjusters forthat antenna element (e.g., signal adjusters 620 and 640, or signaladjusters 630 and 650). Upon receiving the complex weighting, thesesignal adjusters adjust the phase rotation thereby modifying the signalcomponent sent from that antenna element and, consequently, modifyingthe total power of the transmitted signal.

At conditional step 940, the control logic 502 determines whether thepower-control signal for a subsequent time period indicates a decrease,e.g., represented by a down value. If the power-control signal indicatesa decrease, then the adjustment to the phase rotation for the oneantenna element resulted in the basestation receiving the transmittedsignal more optimally. In other words, because the basestation receivedthe transmitted signal with increased total power, the basestation willsend a down indication in a subsequent power-control signal. Thesubscriber communication device can continue to attempt to optimize thephase rotation for that antenna element and simultaneously reduce thetotal power of the transmitted signal. The total power of thetransmitted signal can be reduced because the subscriber communicationdevice is communicating with the basestation in a more optimal manner.

At conditional step 940, if the power-control signal does not indicate adecrease for the total power of the transmitted signal (e.g., thepower-control signal indicates an up value), then the phase rotationadjustment was not effective and the process proceeds to step 950. Atstep 950, logic control 502 changes the phase rotation associated withthat antenna element to the opposite direction. Then, the processproceeds to step 920 where steps 920 through 940 are repeated based onthe opposite direction for the phase rotation.

At conditional step 940, if the power-control signal indicates adecrease for the total power of the transmitted signal (e.g., thepower-control signal indicates a down value), then the phase rotationadjustment was effective and the process proceeds to step 960. At step960, the process is held until the power-control signal reaches a steadystate. At step 970, logic control 502 changes the phase rotationassociated with that antenna element to the same direction. Then, theprocess proceeds to step 920 where steps 920 through 940 are repeatedbased on the same direction for the phase rotation.

FIG. 10 shows a flowchart for calculating the complex weighting byadjusting the phase rotation associated with each antenna element,according to yet another embodiment. At step 1000, the process is helduntil the power-control signal reaches a steady state. Once thepower-control signal reaches a steady state, the process proceeds tostep 1010. At step 1010, the phase rotation associated with one antennaelement is adjusted based of a new complex weighting calculated bycontrol logic 502.

At conditional step 1020, the control logic 502 determines whether thepower-control signal for a subsequent time period indicated a decreasefor the total power of the transmitted power, e.g., represented by adown value. If the power-control signal indicates a decrease, then theadjustment to the phase rotation for the one antenna element resulted inthe basestation receiving the transmitted signal more optimally.Consequently, the selected direction for the phase rotation is correctand further adjustments to the phase rotation in the same direction mayresult in a further optimized transmitted signal.

At conditional step 1020, if the power-control signal does not indicatea decrease for the total power of the transmitted signal (e.g., thepower-control signal indicates an up value), then the phase rotationadjustment was not effective and the process proceeds to step 1030. Atstep 1030, logic control 502 changes the phase rotation associated withthat antenna element to the opposite direction. Then, the processproceeds to step 1000 where steps 1000 through 1020 are repeated basedon the opposite direction for the phase rotation.

At step 1040, logic control 502 changes the phase rotation associatedwith that antenna element in the same direction. At conditional step1050, the control logic 502 determines whether the power-control signalfor a subsequent time period indicated a decrease, e.g., represented bya down value. If the power-control signal indicates a decrease, then theadjustment to the phase rotation was effective and again processproceeds to 1040. Steps 1040 and 1050 are repeated until the controllogic 502 determines that the power-control signal for a subsequent timeperiod indicates an increase for the total power of the transmittedpower. At this point, the optimum phase rotation can be obtained bytaking the average of the phase rotations during step 1040 and theprocess proceeds to step 1060. At step 1060, the phase rotation for theantenna element is returned to the previous optimal phase rotationvalue. Then, the process proceeds to step 1000 where the process isrepeated for another antenna element. In this manner, the process can berepeated for each antenna element to obtain an overall optimum for themultiple antenna elements.

FIG. 11 shows a flowchart for calculating the complex weighting byadjusting the phase rotation associated with each antenna element,according to another embodiment. FIG. 11 describes a method where thetwo most recently received values for the power-control bits are used todetermine the proper phase rotation, and consequently, the propercomplex weighting.

In this embodiment, the subscriber communication device using the CDMAprotocol sends a signal of two adjacent power control groups (PCGs) insuch a manner that the power associated with both PCGs are at the samelevel P. To simplify this discussion, assume for this embodiment thatthe subscriber communication device has two antenna elements, althoughany number of multiple antenna elements is possible. The phase rotationof the second antenna element relative to the first antenna element inthe fast PCG is Phi. The phase rotation of the second antenna elementrelative to the first antenna element in the second PCG is Phi+Delta.

The phase rotation offset (referred to as “Delta”) introduced betweenthe first and second PCG provides a mechanism to determine the directionof the phase rotation between the two antenna elements that will improvethe signal quality received at the basestation. Consequently, thecomplex weighting can be calculated by the following: if the value ofthe power-control bit for the most recent time period corresponds to thevalue of the power-control bit for the second most recent time period,the total power of the transmitted signal is adjusted while maintainingthe phase rotation of the two antenna elements (i.e., maintaining Phi);if the value of the power-control bit for the most recent time perioddiffers from the value of the power-control bit for the second timeperiod, phase rotation of the-two elements (i.e., Phi) is adjusted whilemaintaining the total power of the transmitted signal. The followingmore fully discusses this embodiment.

At step 1100, a phase rotation associated with one of the two antennaelements is initialized. At step 1110, phase rotation offset (alsoreferred to above as Delta) is introduced for two adjacent PCGs. Basedon this introduced phase rotation offset, a transmitted signal is sentfrom the subscriber communication device to the basestation. Then, thebasestation sends a power-control signal based on this receivedtransmitted signal.

At conditional step 1120, a determination is made as to whether the twomost recently received values for the power-control bit are same. Inother words, the power-control bit will have a particular value for eachtime period. For example, this time period for the CDMA and the WCDMAprotocols is 1.25 msec and 666 .mu.sec, respectively. The determinationat step 1120 compares the value for the power-control bit at the mostrecent time period to the value for the power-control bit at the secondmost recent time period. If the two values for the power-control bitcorrespond, the process proceeds to step 1130. If the two values for thepower-control bit differ, the process proceeds to step 1140.

At step 1130, the total power of the transmitted signal is adjustedwhile maintaining the phase rotation for the antenna element. Controllogic 502 adjusts the total power of the transmitted signal andmaintains the phase rotation for the two antenna elements byappropriately calculating new complex weighting. Then, the processproceeds to step 1110 so that the process is repeated.

At step 1140, the phase rotation for the two antenna elements isadjusted while maintaining total power of the transmitted signal.Control logic 502 adjusts the phase rotation for the antenna andmaintains the total power of the transmitted signal by appropriatelycalculating new complex weighting. Then, the process proceeds to step1110 so that the process is repeated.

In this manner, the two most recently received values for thepower-control bits are used to determine the proper phase rotation, andconsequently, a proper complex weighting. Although the total power ofthe transmitted signal is adjusted according to this embodiment, thepower ratios of the respective antenna elements are not adjusted. Theembodiments discussed below in connection with FIGS. 12 and 13 addressthe calculation of complex weighting so that the total power of thetransmitted signal, the phase rotation and the power ratio of theantenna elements are adjusted.

FIG. 12 shows a flowchart for calculating the complex weighting byadjusting the power ratio and the phase rotation associated with eachantenna element, according to an embodiment of the invention. In thisembodiment, an element threshold detection is considered beforeadjusting any phase rotation or power ratio for the antenna elements.Again, to simplify this discussion, assume for this embodiment that thesubscriber communication device has two antenna elements, although anynumber of multiple antenna elements is possible. By checking the ratioof the antenna elements, the basestation can provide feedback using thepower-control bit of the power-control signal.

More specifically, based on the threshold values, the phase rotation canbe adjusted to converge on a substantially optimal phase rotation value.Having determined the substantially optimal phase rotation value, thepower ratio value for the antenna elements can be calculated until asubstantially optimal power ratio value is converged upon. The processis iterative and can be interrupted at any time to change any parameter,such as the phase rotation or the power ratio.

At step 1200, the power ratio for the two antenna elements is measured.At conditional step 1210, a determination is made as to whether thepower ratio is below a predetermined threshold. If the power ratio isnot below the predetermined threshold, then the process proceeds to step1240. If the power ratio is below the predetermined threshold, then theprocess proceeds to step 1220 to tune the phase rotation.

At step 1220, the phase rotation is changed to find a maximum value. Atconditional step 1230, the phase rotation is checked to determinewhether it is a substantially optimal value. If the phase rotation isnot a substantially optimal value, the process proceeds to step 1220where the process for finding a substantially optimal value of the phaserotation continues. If the phase rotation is a substantially optimalvalue, then the process proceeds to step 1240.

At step 1240, the power ratio is changed to find a maximum value. Atconditional step 1250, the power ratio is checked to determine whetherit is a substantially optimal value. If the power ratio is not asubstantially optimal value, the process proceeds to step 1240 where theprocess for finding a substantially optimal value of the power ratiocontinues. If the power ratio is a substantially optimal value, then theprocess proceeds to step 1200, where the overall process repeats.

In sum, the complex weighting can be calculated by adjusting the phaserotation associated with the antenna elements first, and then adjustingthe power ratio associated with the antenna elements. In this manner,both the phase rotation and the power ratio can be adjusted to optimizesubstantially the transmitted signal sent from the subscribercommunication device at received at the basestation.

FIG. 13 shows a flowchart for calculating the complex weighting byadjusting the power ratio and the phase rotation associated with eachantenna element, according to another embodiment of the invention.Similar to FIG. 11, FIG. 13 describes a method where the two mostrecently received values for the power-control bit are used to determinethe proper phase rotation. In FIG. 13, however, the power ratioassociated with the two antenna elements is adjusted after the phaserotation associated with the second antenna element is adjusted. Theprocess of adjusting the power ratio is similar to that described abovefor adjusting the phase rotation in reference to FIG. 11.

In this embodiment, the subscriber communication device using the CDMAprotocol sends a signal of two adjacent power control groups (PCGs) insuch a manner that the power associated with both PCGs are at the samelevel P. Again, to simplify this discussion, assume for this embodimentthat the subscriber communication device has two antenna elements,although any number of multiple antenna elements is possible.

The power ratio associated with the first PCG between the first antennaelement and the second antenna element is Lambda. The power ratioassociated with the second PCG between the first antenna element and thesecond antenna element is Lambda+Zeta. The power ratio offset (i.e.,Zeta) introduced between the first and second PCG provides a mechanismto determine the direction of changing power ration between the twoantenna elements that will improve the signal quality received at thebasestation. Consequently, the complex weighting can be calculated bythe following: if the value of the power-control bit for the mostrecently received time period corresponds to the value of thepower-control bit for the second most recently received time period, thetotal power of the transmitted signal is adjusted while maintaining thepower ratio of the two antenna elements; if the value of thepower-control bit for the most recently received time period differsfrom the value of the power-control bit for the second most recentlyreceived time period, power ratio Lambda is adjusting while maintainingthe total power of the transmitted signal. The following more fullydiscusses this embodiment.

At step 1300, a phase rotation and a power ratio associated with one ofthe two antenna elements is initialized. At step 1310, phase rotationoffset (also referred to above as Delta) is introduced for two adjacentPCGs. Based on this introduced phase rotation offset, a transmittedsignal is sent from the subscriber communication device to thebasestation. Then, the basestation sends a power-control signal based onthis received transmitted signal.

At conditional step 1320, a determination is made as to whether the twomost recently received values for the power-control bit are same. If thetwo values for the power-control bits correspond, the process proceedsto step 1330. If the two values for the power-control bits differ, theprocess proceeds to step 1340.

At step 1330, the total power of the transmitted signal is adjustedwhile maintaining the phase rotation for the antenna element. Controllogic 502 adjusts the total power of the transmitted signal andmaintains the phase rotation for the two antenna elements byappropriately calculating new complex weighting. Note that during thisstep the power ratio for the two antenna elements are also maintained.Then, the process proceeds to step 1310 so that the process is repeated.

At step 1340, the phase rotation for the two antenna elements isadjusted while maintaining total power of the transmitted signal.Control logic 502 adjusts the phase rotation for the antenna andmaintains the total power of the transmitted signal by appropriatelycalculating new complex weighting. Note that during this step the powerratio for the two antenna elements are also maintained. Then, theprocess proceeds to conditional step 1345.

At conditional step 1345, a determination is made as to whether theadjusted phase rotation produced by step 1340 is optimal. If the phaserotation is less than substantially optimal, then the process proceedsto step 1310. If the phase rotation is substantially optimal, then theprocess proceeds to step 1350.

At step 1350, power ratio offset (also referred to above as Zeta) isintroduced for two adjacent PCGs. At conditional step 1350, adetermination is made as to whether the two most recently receivedvalues for the power-control bit correspond. If the two most recentlyreceived values for the power-control bit correspond, the processproceeds to step 1380. If the two most recently received values for thepower-control bit differ, the process proceeds to step 1370.

At step 1370, the power ratio for the antenna element is adjusted whilemaintaining total power of the transmitted signal and maintaining thephase rotation for the two antenna elements. Control logic 502 adjuststhe power ratio for the antenna and maintains the total power of thetransmitted signal and the phase rotation for two antenna elements byappropriately calculating new complex weighting. The process thenproceeds to step 1350 so that steps 1350 and 1360 are repeated until thetwo values for the most recently received values for the power-controlbit correspond.

At step 1380, the power of the transmitted signal is adjusted whilemaintaining the power ratio and the phase rotation for the antennaelement. Control logic 502 adjusts the total power of the transmittedsignal and maintains the power ratio and the phase rotation for theantenna element by appropriately calculating new complex weighting. Atconditional step 1390, a determination is made as to whether the trackis lost. If the track is not lost, then the process proceeds to step1350 so that the process of tuning the power ratio associated with theantenna element and the total power of the transmitted signal arerepeated in steps 1350 through 1390.

Returning to conditional step 1390, if the track is lost, then theprocess proceeds to step 1310 where the process of optimizing the phaserotation and then the power ratio is repeated in steps 1310 through1390.

The above discussion discloses mobile transmit beamforming diversitysystems using a quality-indication signal, which may not require any newstandardized dynamic feedback signaling between the network and themobile unit. The base station receiver may be unaware that the mobileunit is in open loop beamforming transmit diversity mode, i.e., nochanges need to be made to the base station receiver processing(synchronization, channel estimation, demodulation, decoding) in orderto accommodate mobile units in this mode. A similar performance can beachieved by the mobile transmit beamforming with phase shift onlyresulted in phase difference between the first stream and the secondsteam. Some algorithms of determining phase difference from one or morequality-indication signals, i.e., uplink power control bits, arepresented here.

It will be recognized that generally, as discussed above, the phasedifference between the antenna signals may be used to producebeamforming, such that varying a phase difference may change thedirection of the beam formed by constructive interference of thesignals. Accordingly, feedback from the basestation, e.g., in the formof one or more power control bits, may be used to cause increasedperceived power at the basestation by directing the beam to form at thebase station using changes in phase rotation. One method according toembodiments of the invention for maximizing perceived power at thebasestation using phase rotation is described herein.

In some embodiments of the invention, in order to determine a value fora new phase difference, the phase rotation may be varied by successiveadjustments, e.g., −/+δ/2, such that in one transmission the phaserotation is Δ−δ/2, and in a subsequent transmission, the phase rotationis Δ+δ/2. Thus, in one transmission, one antenna may transmit using Φ,and the other antenna one antenna may transmit using phase Φ+Δ−δ/2, andin a second transmission, one antenna may transmit using phase Φ, andthe other antenna one antenna may transmit using Φ+Δ+δ/2. The powercontrol signals corresponding to these two transmissions may bereceived, and compared. If the first transmission resulted in a POWERDOWN, and the second transmission resulted in a POWER UP, then the firsttransmission was received with higher perceived power, and Δ may beincremented in the direction of −δ/2. If the first transmission resultedin a POWER UP, and the second transmission resulted in a POWER DOWN,then the second transmission was received with higher perceived power,and Δ may be incremented in the direction of +δ/2.

Assume that uplink TPC command DOWN is represented by −1, and TPCcommand UP by +1. One beamforming algorithm applying phase change bytest phase change offset, +δ or −δ, every slot and/or by phase changestep, +ε or −ε, every two slots is presented as the following:

-   -   1. Initialize a relative phase between two transmitters,        Δφ=−δ/2, for the first slot.    -   2. Apply test phase change positive offset for next slot,        Δφ′=Δφ+δ.    -   3. Apply test phase change negative offset for next slot,        Δφ″=Δφ′−δ.    -   4. Determine a phase change step from the most two recently        received values of TPC, e.g., TPC1 and TPC2 (corresponding to Δφ        and Δφ′ for the first iteration, or corresponding to Δφ″ and Δφ′        for the second or later iterations), such that:        -   a. if TPC1>TPC2, i.e., TPC1=POWER UP, and TPC2=POWER DOWN,            then the perceived power corresponding to Δφ was weaker than            the perceived power corresponding to Δφ′, and therefore            Δφ=Δφ″+ε.        -   b. if TPC2>TPC1, i.e., TPC1=POWER DOWN, and TPC2=POWER UP,            then the perceived power corresponding to Δφ was stronger            than the perceived power corresponding to Δφ′, and therefore            Δφ=Δφ″−ε.        -   c. otherwise, no change to Δφ, i.e., (Δφ=Δφ″).    -   5. Go to step 2.

If TPC1 and TPC2 are available before step 3, the response latency ofabove algorithm applying phase change step every two slots can befurther reduced by swapping step 3 and step 4 as the following:

-   -   1. Initialize a relative phase between two transmitters,        Δφ=−δ/2, for the first slot.    -   2. Apply test phase change positive offset for next slot,        Δφ′=Δφ+δ.    -   3. Determine a phase change step from the most two recently        received values of TPC, e.g., TPC1 and TPC2 (corresponding to Δφ        and Δφ′), such that:        -   a. if TPC1>TPC2, then Δφ′=Δφ′+ε.        -   b. if TPC2>TPC1, then Δφ′=Δφ′−ε.        -   c. otherwise, no change to Δφ′.    -   4. Apply test phase change negative offset for next slot,        Δφ=Δφ′−δ.    -   5. Go to step 2.

Another beamforming algorithm applying phase change by tested phasechange offset, +δ or −δ, every slot and phase change step, +ε or −ε,every slot is presented as the following:

-   -   1. Initial relative phase between two transmitters, Δφ=−δ/2, for        the first slot.    -   2. Apply test phase change positive offset for the next slot,        Δφ′=Δφ+δ.    -   3. Apply test phase change negative offset for the next slot,        Δφ″=Δφ′−δ.    -   4. Determine a phase change step from the most two recently        received values of TPC, e.g., TPC1 and TPC2 (corresponding to Δφ        and Δφ′), such that:        -   a. if TPC1>TPC2, Δφ=Δφ″+ε.        -   b. if TPC2>TPC1, Δφ=Δφ″−ε.        -   c. otherwise, no change to Δφ, i.e., (Δφ=Δφ″).    -   5. Apply test phase change offset for next slot, Δφ′=Δφ+δ.    -   6. Determine new phase change step from the most two recently        received values of TPC, e.g., TPC1 and TPC2 (corresponding to        Δφ′ and Δφ″), such that:        -   a. if TPC1>TPC2, Δφ=Δφ′−ε.        -   b. if TPC2>TPC1, Δφ=Δφ′+ε.        -   c. otherwise, no change to Δφ, i.e., (Δφ=Δφ′).    -   7. Apply test phase change offset for next slot, Δφ″=Δφ−δ.    -   8. Determine new phase change step from the most two recently        received values of TPC, e.g., TPC1 and TPC2 (corresponding to        Δφ″ and Δφ′), such that:        -   a. if TPC1>TPC2, Δφ=Δφ″+ε.        -   b. if TPC2>TPC1, Δφ=Δφ″−ε.        -   c. otherwise, no change on Δφ, i.e., (Δφ=Δφ″).    -   9. Go to step 5.

If TPC1 and TPC2 are available before step 3, the response latency ofabove algorithm applying phase change step every slot can be furtherreduced by swapping step 3 and step 4 as the following:

-   -   1. Initial relative phase between two transmitters, Δφ=−δ/2, for        the first slot.    -   2. Apply test phase change positive offset for the next slot,        Δφ′=Δφ+δ.    -   3. Determine a phase change step from the most two recently        received values of TPC, e.g., TPC1 and TPC2 (corresponding to Δφ        and Δφ′), such that:        -   a. if TPC1>TPC2, Δφ′=Δφ′+ε.        -   b. if TPC2>TPC1, Δφ′=Δφ′−ε.        -   c. otherwise, no change to Δφ′.    -   4. Apply test phase change negative offset for the next slot,        Δφ=Δφ′−δ.    -   5. Determine new phase change step from the most two recently        received values of TPC, e.g., TPC1 and TPC2 (corresponding to        Δφ′ and Δφ), such that:        -   a. if TPC1>TPC2, Δφ=Δφ′−ε.        -   b. if TPC2>TPC1, Δφ=Δφ′+ε        -   c. otherwise, no change to Δφ, i.e., (Δφ=Δφ′).    -   6. Go to step 2.

Phase shift applied to both the first stream and to the second streamcan be distributed in many ways to create the same phase differencechange, Δφ=Δφ±δ±ε. For example, φ₁=φ₁+δ/2 and φ₂=φ₂−δ/2±ε, or φ₁=φ₁−δ/2and φ₂=φ₂+δ/2±ε. Another example of distributing phase shift change isφ₂=φ₂±δ/2±ε/2 and φ₁=−φ₂.

Phase shift can also be applied to the second stream only. For example,φ₁=0 and φ₂=Δφ.

Here, test phase change offset is applied every slot and new phasechange step is determined from two most recently received TPC. However,without loss of generality, test phase change offset can be appliedevery two, three or more slots, and new phase change step can bedetermined from more than two most recently received TPC. For example,test phase change offset is applied every two slots and new phase changestep is determined from four most recently received TPC.

The absolute value of test phase change offset, |δ|, may be greater thanor equal to the absolute value of phase change step, |ε|. The ratiobetween |δ| and |ε| may be 1, or it may be 2, or it may be 3, or it maybe 4.

The absolute value of test phase change offset, |δ|, may be greater thanor equal to the absolute value of phase change step, |ε|. Thus, forexample, |δ| may be equivalent to |ε|. Accordingly, in one example, |δ|and |ε| may be a number between 5 and 20 degrees; in another example,|δ| and |ε| may be a number between 10 and 15 degrees; in yet anotherexample, |δ| and |ε| may be 12 degrees.

The absolute value of test phase change offset, |δ|, may be greater thanor equal to two times the absolute value of phase change step, |ε|.Accordingly, in one example, |δ| may be a number between 10 and 40degrees, and 10 may be half that number, e.g., a number between 5 and 20degrees; in another example, |δ| may be a number between 20 and 30degrees, and |ε| may be half that number, e.g., a number between 10 and15 degrees; in yet another example, |δ| may be 24 degrees and |ε| may be12 degrees.

The absolute value of test phase change offset, |δ|, may be greater thanor equal to four times the absolute value of phase change step, |ε|.Accordingly, in one example, |δ| may be a number between 20 and 80degrees, and |ε| may be a quarter of that number, e.g., a number between5 and 20 degrees; in another example, |δ| may be a number between 40 and60 degrees, and |ε| may be a quarter of that number, e.g., a numberbetween 10 and 15 degrees; in yet another example, |δ| may be 48 degreesand |ε| may be 12 degrees.

It will be recognized that in order to obtain accurate feedback usingthe TPC information, it is desirable that the UE should be able to matchthe TPC information with the transmission to which the base stationresponded. That is, for proper operation, the algorithm should be ableto correctly match between UE phase perturbations and TPCs received fromthe BTS; specifically, the boundary between −/+ pairs needs to bedetermined correctly. That is, the TPC for Δφ−δ should be identified,and the TPC for Δφ+δ should be identified. However, different basestations and protocols may cause different delays between the UE'stransmission and receipt of the base station response with a TPCcommand. Accordingly, in some embodiments of the invention, a UE mayidentify a protocol and/or possibly a manufacturer or model of the basestation, and look up an appropriate delay. Thus, for example,identifying a protocol/manufacturer/model may result in considering adelay of 1 slot, or 2 slots, or 3 slots. The delay parameter may beconsidered in matching the TPC to the diversity transmission parameter.Thus, if a delay parameter is 1 slot, then a received TPC may beconsidered as corresponding to the immediately previous transmission.Similarly, if a delay parameter is 2 slots, then a received TPC may beconsidered as corresponding not to the immediately previoustransmission, but the second-to-last transmission. Finally, if a delayparameter is 3 slots, then a received TPC may be considered ascorresponding not to the last or second-to-last transmission, but to thethird-to-last transmission.

The determination of the delay parameter may be made upon registrationonto a network. For example, upon registration to a network, the UE mayidentify the network protocol, and make/model of the base station, thenusing a look-up table stored in its memory, the UE will identify thecorrect delay mentioned above and set it accordingly. Other methods ofdetermining the appropriate delay may be possible. For example, the UEmay conduct a test and measure the response time of the base station.

In addition, as the network and/or base station may change due tomobility of the UE, a similar procedure for determining the delayparameter may be repeated periodically each time the registration isaltered.

While various embodiments of the invention have been described above, itshould be understood that they have been presented by way of exampleonly, and not limitation. Thus, the breadth and scope of the inventionshould not be limited by any of the above-described embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

The previous description of the embodiments is provided to enable anyperson skilled in the art to make or use the invention. While theinvention has been particularly shown and described with reference toembodiments thereof, it will be understood by those skilled in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention. For example,although the previous description of the embodiments often referred tocommunication devices using a CDMA protocol, other types of protocolsare possible. For example, the communication devices similar to thosedescribed above can be used with time-division multiple access (TDMA) orfrequency-division multiple access (FDMA) protocols. Such a TDMAprotocol can include, for example, the Global Systems for MobileCommunications (GSM) protocol.

Note that although the tuning of a communication device is describedthrough the use complex weighting, in other embodiments other types ofcontrol signals can tune the communication device. In other words, thetuning of a communication device through the use such control signalsneed not be limited to information about varying the magnitude and phaseof the signal. For example, the control signals can carry information tovary the magnitude, phase, frequency and/or timing of the signalassociated with each antenna element.

We claim:
 1. A mobile communication device comprising: a processor toproduce a data signal and a value of a transmit diversity parameter; avector modulator to produce first and second signals based on said datasignal, said first signal differing from second signal based on saidvalue of the transmit diversity parameter; first and second antennas totransmit said first and second signals, respectively, wherein saidmobile communication device is to receive from a receiving communicationdevice a signal quality indication pertaining to quality of the combinedfirst and second signals as received at the receiving communicationdevice, wherein said processor is to determine based at least on saidsignal quality indication a modified value of said transmit diversityparameter, wherein said vector modulator is to produce said first andsecond modified signals, said first modified signal differing from saidsecond modified signal based on said modified value of the transmitdiversity parameter, wherein said vector modulator is to modify saidfirst signal by modifying a transmission parameter thereof in a firstdirection, and wherein said vector modulator is to modify said secondsignal by modifying said transmission parameter thereof in a seconddirection, opposite to said first direction, and wherein said first andsecond antennas are to transmit said modified first and second signals,respectively.
 2. The mobile communication device of claim 1, wherein thesignal quality indication is a power control signal sent from thereceiving communication device to the mobile communication device. 3.The mobile communication device of claim 1, wherein the transmitdiversity parameter is a phase difference between a signal transmittedusing the first antenna and a signal transmitted using the secondantenna, and wherein the transmission parameter is a phase.
 4. Themobile communication device of claim 3, wherein said processor is toproduce a first phase difference value based on an initial nominal phasedifference value, and wherein said vector modulator is to produce firstand second signals differing based on said first phase difference value,wherein said vector modulator is to modify the phase of the first signalin a first direction, and to modify the phase of the second signal in asecond direction, opposite to said first direction; wherein said mobilecommunication device is to receive from the receiving communicationdevice a first signal quality indication pertaining to quality of thecombined first and second signals differing based on the first phasedifference value as received at the receiving communication device;wherein said processor is to produce a second phase difference value,and wherein said vector modulator is to produce first and second signalsdiffering based on said second phase difference value, wherein saidvector modulator is to modify the phase of the first signal in thesecond direction, and to modify the phase of the second signal in thefirst direction; wherein said mobile communication device is to receivefrom the receiving communication device a second signal qualityindication pertaining to quality of the combined first and secondsignals differing by the second phase difference value as received atthe receiving communication device; wherein said processor is todetermine the modified phase difference value based on a phase changestep to the initial nominal phase difference value, wherein thedirection of said phase change step from the initial nominal phasedifference value is based at least on said first and second signalquality indications; and wherein said first and second antennas are totransmit a data signal based on the modified nominal phase differencevalue.
 5. The mobile communication device of claim 4, wherein thedifference between the first and second phase difference values is aphase change offset value, and wherein the initial nominal phasedifference is half of the phase change offset value greater than one ofthe first and second phase difference values and half of the phasechange offset value less than the other of the first and second phasedifference values.
 6. The mobile communication device of claim 5,wherein the magnitude of the phase change offset is greater than orequal to the magnitude of the phase change step.
 7. The mobilecommunication device of claim 6, wherein the magnitude of the phasechange offset and the magnitude of the phase change step are eachbetween 5 and 20 degrees.
 8. The mobile communication device of claim 6,wherein the magnitude of the phase change offset and the magnitude ofthe phase change step are each between 10 and 15 degrees.
 9. The mobilecommunication device of claim 6, wherein the magnitude of the phasechange offset and the magnitude of the phase change step are each 12degrees.
 10. The mobile communication device of claim 5, wherein themagnitude of the phase change offset is greater than or equal to twotimes the magnitude of the phase change step.
 11. The mobilecommunication device of claim 10, wherein the magnitude of the phasechange offset is between 10 and 40 degrees, and the magnitude of thephase change step is between 5 and 20 degrees.
 12. The mobilecommunication device of claim 10, wherein the magnitude of the phasechange offset is between 20 and 30 degrees, and the magnitude of thephase change step is between 10 and 15 degrees.
 13. The mobilecommunication device of claim 10, wherein the magnitude of the phasechange offset is 24 degrees, and the magnitude of the phase change stepis 12 degrees.
 14. The mobile communication device of claim 5, whereinthe magnitude of the phase change offset is greater than or equal tofour times the magnitude of the phase change step.
 15. The mobilecommunication device of claim 14, wherein the magnitude of the phasechange offset is between 20 and 80 degrees, and the magnitude of thephase change step is between 5 and 20 degrees.
 16. The mobilecommunication device of claim 14, wherein the magnitude of the phasechange offset is between 40 and 60 degrees, and the magnitude of thephase change step is between 10 and 15 degrees.
 17. The mobilecommunication device of claim 14, wherein the magnitude of the phasechange offset is 48 degrees, and the magnitude of the phase change stepis 12 degrees.
 18. A method of modifying a signal transmitted by amobile communication device comprising: transmitting first and secondsignals from first and second antennas, respectively, said first signaldiffering from second signal based on a first value of a transmitdiversity parameter; receiving a signal quality indication from areceiving communication device, said signal quality indicationindicating a signal quality of the combined first and second signals asreceived at said receiving communication device; determining based atleast on said signal quality indication a modified value of saidtransmit diversity parameter, producing first and second modifiedsignals, said first modified signal differing from said second modifiedsignal by said modified value of the transmit diversity parameter bymodifying a transmission parameter of said first signal in a firstdirection, and modifying the transmission parameter of said secondsignal in a second direction, opposite to said first direction; andtransmitting said first and second modified signals on said first andsecond antennas, respectively.
 19. The method of claim 18, wherein thesignal quality indication is a power control signal sent from thereceiving communication device to the mobile communication device. 20.The method of claim 18, wherein the transmit diversity parameter is aphase difference between a signal transmitted using the first antennaand a signal transmitted using the second antenna, and wherein thetransmission parameter is a phase.
 21. The method of claim 20,comprising: producing a first phase difference value based on an initialnominal phase difference value by producing first and second signalsdiffering based on said first phase difference value, wherein the phaseof the first signal is modified in a first direction, and the phase ofthe second signal is modified in a second direction, opposite to saidfirst direction; receiving from the receiving communication device afirst signal quality indication pertaining to quality of the combinedfirst and second signals differing by the first phase difference valueas received at the receiving communication device; producing a secondphase difference value based on the initial nominal phase differencevalue by producing first and second signals differing based on saidsecond phase difference value, wherein the phase of the first signal ismodified in the second direction, and the phase of the second signal ismodified in the first direction; receiving from the receivingcommunication device a second signal quality indication pertaining toquality of the combined first and second signals differing by the secondphase difference value as received at the receiving communicationdevice; determining the modified phase difference value based on a phasechange step to the initial nominal phase difference value, wherein thedirection of said phase change step from the initial nominal phasedifference value is based at least on said first and second signalquality indications; and transmitting a data signal based on themodified nominal phase difference value.
 22. The method of claim 21,wherein the difference between the first and second phase differencevalues is a phase change offset value, and wherein the initial nominalphase difference is half of the phase change offset value greater thanone of the first and second phase difference values and half of thephase change offset value less than the other of the first and secondphase difference values.
 23. The method of claim 22, wherein themagnitude of the phase change offset is greater than or equal to themagnitude of the phase change step.
 24. The method of claim 23, whereinthe magnitude of the phase change offset and the magnitude of the phasechange step are each between 5 and 20 degrees.
 25. The method of claim23, wherein the magnitude of the phase change offset and the magnitudeof the phase change step are each between 10 and 15 degrees.
 26. Themethod of claim 23, wherein the magnitude of the phase change offset andthe magnitude of the phase change step are each 12 degrees.
 27. Themethod of claim 22, wherein the magnitude of the phase change offset isgreater than or equal to two times the magnitude of the phase changestep.
 28. The method of claim 27, wherein the magnitude of the phasechange offset is between 10 and 40 degrees, and the magnitude of thephase change step is between 5 and 20 degrees.
 29. The method of claim27, wherein the magnitude of the phase change offset is between 20 and30 degrees, and the magnitude of the phase change step is between 10 and15 degrees.
 30. The method of claim 27, wherein the magnitude of thephase change offset is 24 degrees, and the magnitude of the phase changestep is 12 degrees.
 31. The method of claim 22, wherein the magnitude ofthe phase change offset is greater than or equal to four times themagnitude of the phase change step.
 32. The method of claim 31, whereinthe magnitude of the phase change offset is between 20 and 80 degrees,and the magnitude of the phase change step is between 5 and 20 degrees.33. The method of claim 31, wherein the magnitude of the phase changeoffset is between 40 and 60 degrees, and the magnitude of the phasechange step is between 10 and 15 degrees.
 34. The method of claim 31,wherein the magnitude of the phase change offset is 48 degrees, and themagnitude of the phase change step is 12 degrees.